Engine What Are Some Tips To Build A Long Lasting Reliable 347!!!

This last fall i bought this 4 eyed 86 gt with 347 and 10,000 on the motor. It had lots of power during test drive and seemed to have good compression. It sounded great.Had high oil pressure and everything seemed pretty good on it. After i got it home and drove it for a week it and after testing out down a few strait stretches it started to smoke some. One day gave my friend a ride in it to show off and couldn't resist myself and she blew!!
A valve broke off and dropped one down on my piston at about 6,500 rpm! (has a cam designed to rev that high by the way). Not sure why it broke off. The car has afr 185, and i sent the head that had the damage to get welded. I am guessing that the head had afr valves. Didn't see any valve float problems on any of the other pistons. Can valves go bad and just break off like that?
Anyway my question is what are some tips to rebuild this motor and avoid problems like this happening again? I have a guy that i know that is going put the motor together for me. He is mostly a chevy guy but how do you know if people working on your motor actually know what they are doing? I don't have any race shops around where i live and this seems to be the only option. Just looking for tips on building motors so they have good reliabe power. Also last and i can feel safe opening them up every one in a while and not worrying about it going to blow up or something

SN Certified TechnicianMod Dude

Unfortunalty things of this nature just sometimes happen. To prevent it, rebuild it with care and use all good parts. Where did the valve break? locks or retainers still ok or did they break too? These motors are generally reliable with good parts. I would be curious to see some more pictures of the damaged parts, maybe that could leed some insight into what exactly caused it to break.

Carnage.... I love it! I had the same thing happen to one of my street bikes. All stock motor but I guess one of the valves got over stressed. Chit happens I guess and theres nothing you can do about it. Put it all back together with quality parts and beat it till you get tired!!! Sometimes you just can't question mechanical failure.

for sure doing a valve job on the heads lol, here is what i am planning on replacing to help prevent this from happening. scorpion rockers, ethier springs from ed curtis or comp not sure yet, probably some plasma molly rings, not sure if i should replace roller lifters they got 10000 on them?
what do you guys think?

we went pretty damn fast on an off the shelf 347 eagle forged rotating assembly and ross pistons.
(4.83@152 with a small ass street car cam)
and we went really damn fast on an eagle crank GRP rods and ross pistons. (7.37@191 with the custom bullet cam and the valves floating at 9300+)

so i dont think everything needs to be over built. i wouldnt do stuff like cast crank and pistons but i wouldnt go ordering custom coated diamond pistons and a billet crank.

Founding Member

we went pretty damn fast on an off the shelf 347 eagle forged rotating assembly and ross pistons.
(4.83@152 with a small ass street car cam)
and we went really damn fast on an eagle crank GRP rods and ross pistons. (7.37@191 with the custom bullet cam and the valves floating at 9300+)

so i dont think everything needs to be over built. i wouldnt do stuff like cast crank and pistons but i wouldnt go ordering custom coated diamond pistons and a billet crank.

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in other words you did the things on my list. i never suggested diamond pistons or a billet crank, and unless one is going racing, i would never suggest a billet crank. cast pistons and cast cranks are fairly tough to begin with when quality castings are made, and hypereutectic pistons are stronger still, and forged are about the toughest on the market.

but if you had any reading comprehension skills, you would have noted that i said use top quality products, and i said that if you dont think you need forged piston, use them anyway.

in other words you did the things on my list. i never suggested diamond pistons or a billet crank, and unless one is going racing, i would never suggest a billet crank. cast pistons and cast cranks are fairly tough to begin with when quality castings are made, and hypereutectic pistons are stronger still, and forged are about the toughest on the market.

but if you had any reading comprehension skills, you would have noted that i said use top quality products, and i said that if you dont think you need forged piston, use them anyway.

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with the motors i deal with eagle rods and crank arent top quality by any means. but we still went pretty damn fast with it and it lived till it started to float a valve from having a miss matched cam and spring set up.

top quality stuff would be stuff like a $2000 callies magnum crank and oliver rods.

Dang rbobm. You read more Into that comment than I did. I think he was just expanding on what you said. Why so touchy?

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i think a lot of people have a different idea of what "top quality" parts are compared to what i do.

most people would see what the turbo car motor use to be as top shelf stuff. but it was junk in my eyes with some ok stuff.
eagle crank and rods ross pistons trick flow high ports trick flow rockers with a stud girdle dart block roll master timing chain. to me this has some ok stuff. but its nothing over the top
the nitrous motor on the other hand is top shelf stuff... best of everything
RDI aluminum block ford racing SC1's by bennett racing ford racing intake for those heads titanum valves locks and retainers danny bee belt drive GRP aluminum rods custom diamond coated pistons jesel rockers stock car products dry sump oil pump moroso vac pump ( and if it some out of retirement it will get a new star racing pump) 50mm roller cam bearing 9/16" head studs O ringed block with copper head gaskets.

Founding Member

Dang rbobm. You read more Into that comment than I did. I think he was just expanding on what you said. Why so touchy?

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he was making the assumption that i was talking about going to parts that made from unobtanium for everything, in other words build a race engine for the street. and that wasnt what i meant. for instance if one is doing a heavy duty street build, and they are going to use a blower pushing lets say 6psi boost, you can get away with good TRW cast pistons, but i recommend stepping up to good TRW forged pistons. its called common sense building, not throwing all kinds of money at a build that doesnt require it.

top quality for most people means getting the best parts for the application.

My reference to the race car shows you don't need anything special to make big power and stay together. The parts in it at first were nothing special. It started life as a well built street car motor then got a turbo by the first owner.

My idea of top quality parts isn't what most people on here think of as top quality stuff... that's all I'm getting at

Are you putting it back into a stock block? If so any aftermarket forged piston,rod and cast crank will work. Don't worry about forged rods/crank because a cast crank will out last the block. Proper clearances/machining/assembling will go a loooong way into the longevity of the engine. Arp bolts,studs, good gaskets,mellings oil pump & pickup,clevite bearings,etc.

well i am getting a different block because the one i have now is cracked, but i am debating about buying a shortblock or buying a new piston and rod and installing the rotating assembly into a different block because i am kinda tight on money

well i am getting a different block because the one i have now is cracked, but i am debating about buying a shortblock or buying a new piston and rod and installing the rotating assembly into a different block because i am kinda tight on money

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By "stock block" I mean a 2 bolt mains block that isn't an aftermarket block like a Dart,FMS Boss,etc. I'm assuming yes. Especially with the "budget" comment. Some places you can look for a shortblock are Ford Strokers.com,DSS racing,CHP,and a bunch of others. Most are around 2500$

ya i am looking at some of those. I think it would be nice to have a motor built by pros that do it all the time like they do, but i could get away with just buying a new piston and rod and stock block from junk yard but i am kinda nervous about it not getting built properly and it may start to use oil and blow up again someday